On 08/27/2015 10:42 PM, Jason Wang wrote:

On 08/27/2015 06:43 PM, Michael S. Tsirkin wrote:

quoted

On Wed, Aug 26, 2015 at 01:45:30PM +0800, Jason Wang wrote:

quoted

On 08/26/2015 12:32 AM, Vlad Yasevich wrote:

quoted

On 08/25/2015 07:30 AM, Jason Wang wrote:

quoted

On 08/25/2015 06:17 PM, Michael S. Tsirkin wrote:

quoted

On Mon, Aug 24, 2015 at 04:33:12PM +0800, Jason Wang wrote:

quoted

quoted

For macvlan, switch to use IFF_NO_QUEUE instead of tx_queue_len = 0.

For macvtap, after commit 6acf54f1cf0a6747bac9fea26f34cfc5a9029523
("macvtap: Add support of packet capture on macvtap
device."). Multiqueue macvtap suffers from single qdisc lock
contention. This is because macvtap claims a non zero tx_queue_len and
it reuses this value as it socket receive queue size.Thanks to
IFF_NO_QUEUE, we can remove the lock contention without breaking
existing socket receive queue length logic.

Cc: Patrick McHardy <redacted>
Cc: Vladislav Yasevich <redacted>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

Seems to make sense. Give me a day or two to get over the jet lag
(and get out from under the pile of mail accumulated while I was traveling),
I'll review properly and ack.

A note on this patch: only default qdisc were removed but we don't lose
the ability to attach a qdisc to macvtap (though it may cause lock
contention on multiqueue case).

Wouldn't that lock contention be solved if we really had multiple queues
for multi-queue macvtaps?

-vlad

Yes, but this introduce another layer of txq locks contention?

I don't follow - why does it? Could you clarify please?

I believe Vlad wants to remove NETIF_F_LLTX. If yes, core will do an
extra tx lock at macvlan layer.

No, I don't want to remove it.  In a sense, it would function similar to
how it works when fwd_priv is populated.  I am still testing the code
as it's showing some strange artifacts...  could be due to keeping LLTX.

-vlad

quoted

quoted

And it
also needs macvlan multiqueue support. We used to do something like this
but switch to NETIF_F_LLTX finally. You may refer:

2c11455321f37da6fe6cc36353149f9ac9183334 macvlan: add multiqueue capability
8ffab51b3dfc54876f145f15b351c41f3f703195 macvlan: lockless tx path

My concern is that the moment someone configures a non-standard qdisc
scalability suddenly disappears. That would also be tricky to debug in the
field as not a lot of developers use non-standard qdiscs.
What do you think?

Probably not an issue. Non-standard qdisc may need be attached manually
after device creation, and we don't lose this ability with this patch.
(Unless somebody changes default_qdisc). Actually, user before
6acf54f1cf0a6747bac9fea26f34cfc5a9029523 does not expect any qdisc work
for macvtap like other stacked devices. This patch also restore this.